Verified answer

See drawing below

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For a rhombus the area is half the product of the diagonals

Area = (Diagonal 1 * Diagonal 2) / 2

We are given diagonal RO as 13.8"

Draw in diagonal MH

this creates right triangle CHO

CH = (13.8/2) * tan 56

CH = 10.229670682737908

Since CH is half of diagonal MH

Area = 13.8 * 10.229670682737908

Area = 141.1694554218

Area ≈ 141.17 in² <–––––––

The area formula if you have had it is A = a b sin C where a and b are two sides and C is the included angle.

Have you had the law of cosines? If so call the sides x. You get 13.8² = x² + x² - 2xx cos 68

2x² - 2x² cos 68 - 13.8² = 0

x = 12.339212... so plug that in for x • x • sin 68